The present invention relates to a universal joint used in the steering apparatus or the like of an automobile, and, more particularly, to a technique designed to simplify the structure and reduce the manufacturing cost thereof.
The steering apparatus of an automobile or the like comprises a steering wheel that provides the driver with the steering operations, a steering gear that steers the vehicle's wheels, and a steering shaft that provides a linkage between the steering wheel and the steering gear. With the steering apparatus for an automobile, it is common to use a plurality of shafts coupled together axially by universal joints, because there is limited chance for locating the steering gear on the central axial line of the steering wheel.
A Cardan joint in which a crosspiece (cross-shaped axes) is inserted in a freely oscillatory manner between a pair of joint yokes is generally used as a universal joint for a steering shaft, as disclosed in U.S. Pat. No. 3,501,928. In this Cardan joint, end portions of steering shafts are connected to the free ends of the two joint yokes, and needle bearings are disposed between the crosspiece and the joint yokes. U.S. Pat. No. 4,579,546 discloses a universal joint in which a hub is interposed between each joint shaft and the joint yoke, and these components are connected together by one long pin and two short pins. Otherwise, Japanese Utility Model Publication(KOKOKU) No. 4-48339 discloses a universal joint that uses a spherical joint member and Japanese Patent Laid-Open Application(KOKAI)No. 1-169123 discloses a universal joint that uses an annular joint element.
Universal joints of the prior art have a problem in that it is difficult to reduce the manufacturing costs thereof, or to apply them to mass-production. For example, the previously mentioned Cardan joint requires a crosspiece and four needle bearings in addition to the pair of joint yokes, which are subjected to machining after being forged (or cast), so it is inevitable that a larger number of components and a larger number of assembly steps are required. In addition, the shapes of the joint shafts and joint yokes in the universal joint disclosed in U.S. Pat. No. 4,579,546 are extremely complicated, so that a larger number of steps and a longer time is required for machining and other processing, thus leading to an increase in manufacturing cost and a decrease in productivity. The other universal joints are similarly undesirable for various reasons, such as the complicated shapes of the spherical joint member or joint yoke, or a larger number of components.
The present invention was devised in the light of the above situation and has the objective of providing a universal joint that has a simpler structure and a reduced manufacturing cost.